The present invention relates to a method for surface treating a portion of the surface of a small article. More particularly, the present invention relates to an improved method for coating, etching, or coloring a portion of a small spherical article by substantially supporting the small spherical article by the surface tension of the treating solution.
Many small spherical particles are required for the manufacture of a magnetic particle display panel disclosed in my copending patent application Ser. No. 566,455, filed Apr. 9, 1975 and now abandoned which is incorporated herein by reference. These spherical particles might range from approximately 10 microns to the order of 200 microns in diameter depending upon the desired resolution of the display panel. It is desirable to have the small spherical particles reflect a different color from a portion of the particle than from other portions of the particle in order to provide contrast in the presentation of the display panel.
One possible method to coat or color one area of a spherical particle would be to spray that area of the particle from a fixed position with relationship to the particle. The spherical particle would serve as a mask for the remainder of the particle and only the portion of the particle facing the sprayer would be coated. However, such a method is not satisfactory for a particle useable in the display panel because of the gradual transition from the coated portion to the uncoated portion. For applications in the magnetic particle display panel, it is desirable for the different coated or colored portions to have a clear and precise separation of colored areas. In the past, many different approaches have been proposed for coating or coloring one area of an article. One such method proposes placing the article on an adhesive tape and then spraying the exposed area of the article. This method is very satisfactory for certain articles that tend to be flat, however, it is not satisfactory for spherical particles because once again the transition area between the portion coated and the portion that is uncoated is not sharply defined. Another method proposed in the past is to dip an article to be coated into a coating solution. The article can be hand held or hung from a conveyor while the article is dipped in and out of the coating solution. This method seems to work well for large articles or for articles that can be easily attached to a conveyor belt arrangement and moved in and out of a coating solution. However, for a small spherical particle it would not be practical, since it would be rather difficult to hold a small spherical particle and dip only the desired portion into a coating solution. One of the more practical methods for coating one half of a sphere or a definite portion of the sphere is proposed in U.S. Pat. No. 2,740,375 which issued to W. H. Diehl, et al. This patent proposes a method wherein the spherical particle is held between two adjacent discs with one of the discs having an opening cut out over the spherical particle so that the exposed area of the spherical particle can be sprayed. Although this approach seems to have practical application to larger sized spheres, it would be somewhat impractical for the large number of small spherical particles required in a single magnetic particle display panel. Although many of the prior art methods appear to have application for their intended purpose, none of them lend themselves to properly coating or coloring large numbers of small particles.
In view of the foregoing, it should now be understood that it would be desirable to provide an improved method for treating the surface of small particles that would solve the above and other problems.
Accordingly, one of the objects of the present invention is to provide an improved method for coating or coloring a definitely defined area of a small article so that a sharply visible transition is readily apparent between the coated and uncoated areas.
Another object of the invention is to provide an improved method for coloring a predetermined well defined area of a magnetized small spherical particle.
Yet another object of the present invention is to provide an improved method for coloring a desired portion of a small article which takes advantage of the surface tension of the treating solution on which to support the small article.